JAMB Physics Past Questions & Answers - Page 29

141.

In a series R-L-C circuit at resonance, the voltages across the resistor and the inductors are 30V and 40V respectively. What is the voltage across the capacitor?

30V

40V

50V

70V

View answer & explanation

Correct answer is B

AT resonance; X\(_{L}\) = X\(_{c}\)

\(\therefore\) = V\(_{L}\) = V\(_{c}\) = 40V

142.

Calculate the heat energy required to vaporize 50g of water initially at 80ºC if the specific heat capacity of water is 4.23jg\(^{-1}\)k\(^{-1}\) (specific latent heat of vaporization of water is 2260jg\(^{-1}\)

530000J

23200J

17200J

130000J

View answer & explanation

Correct answer is D

H = mc\(\bigtriangleup\theta\) + mL

H = ?

m = 50g, c = 4.23J/gk,L = 2260, \(\bigtriangleup\theta\) = 80ºC

H = 50 [4.23 x 80 + 2260]

= 129920 \(\approx\) 130,000J

143.

Which of the following is not a vector quantity?

momentum

force

temperature

displacement

View answer & explanation

Correct answer is C

displacement, velocity, and acceleration, linear momentum, force are vector quantities, while speed (the magnitude of velocity), time, and mass are scalars. To qualify as a vector, a quantity having magnitude and direction must also obey certain rules of combination.

144.

A boy standing some distance from the foot of a tall cliff claps his hands and hears an echo 0.5s later. If the speed of sound is 340ms\(^{-1}\), how far is he from the cliff?

680m

170m

34m

85m

View answer & explanation

Correct answer is D

V = \(\frac{2d}{t}\)
v = 340ms\(^{-1}\)
t = 0.5s
d= ?

d = \(\frac{2d}{2} = \frac{340 \times 0.5}{2}\) = 85m

145.

A source of sound produces waves in air of wavelength 1.65m. If the speed of sound in air is 330ms\(^{-1}\), the period of vibration in air is?